doc/code.html: fix broken dashboard link         Fixes issue 3420.         Part of issue 3424.
doc/code.html: fix broken dashboard link
        Fixes issue 3420.
        Part of issue 3424.

R=golang-dev, cldorian, adg, r
CC=golang-dev
http://codereview.appspot.com/5958046

h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang